[mythtv-users] Output to HDTV

[Peter Lee]

On Sat, 03 Jan 2004, Shane Warren wrote:
> 
> Peter Lee wrote:
> 
>> This is possibly unrelated, but:  Are you sure this is a (de)interlacing
>> problem?  I am also running with a GF4MX (440) on an nForce2 board.  What I
>> find is that if I have twinview enabled then I get pretty annoying tearing
>> of the image (especially during fast panning).  As far as I can tell (from
>> googling around), my video card is not able to do vsync properly when
>> twinview is enabled.  This affects any video application (mplayer, xine,
>> etc), even if the application's vsync and double-buffering options are
>> enabled.
>>  
>> 
> I actually have my DLP rear projector hooked up through straight VGA
> right now, as soon as my new card arrives next week I will be using
> DVI.  Right now DVDs look unbelievably excellent (at 1280x720p), no
> tearing as I see on interlaced video from the tuner cards.  At the
> moment I'm not using twinview, the onboard on my nforce2 board only has
> VGA out, so I bought an GF4MX440 w/ svideo, vga, and dvi out, mainly so
> I could get DVI out and also try the twinview out svideo out.   So I'm
> not 100% sure its an interlacing problem, but lets say I'm 99% :-)  What
> I don't get is why some people w/ hdtvs don't seem to have the
> interlacing problem, my current theory is that most people are running
> at 540p which most hdtvs may de-interlace since it may take it as 1080i,
> again this is just a theory, or maybe your TVs are always de-interlacing
> even if its a progressive input (seems unlikely).

Hmm...yes, this does appear to be an interlacing problem.  And I can't
explain why I )and others) am not experiencing the same problem (as long as
twinview is not enabled in my XFConfig file).  I guess my thought was that
the application (myth) was doing the deinterlacing (through tv playback
setup option in mythfrontend) and that this was making everything OK (as it
definitely appears to be for my setup).  But I suspect that my understanding
of this is below yours, so I may be wrong about this.

> My understanding of this is that if you display an interlaced video on a
> non interlaced display you are sure to get interlacing effects unless
> the monitor device deinterlaces it or the output device deinterlaces
> it.  BTW is the interlacing effect is really like a tearing from a non
> vsync display, the best way I describe an interlacing effect is you see
> a bunch of horizontal lines through objects especially when they move
> quickly? 

Yes, when I run twinview, I get exactly this kind of tearing, on both the
vga and svideo outputs.  For example, if the camera pans during a football
game, I will often see an effect that looks like the players are getting cut
in half...

> I'm sorry to hear that twinview has a different way to screw up video,
> hopefully I can make my new card work, if not I'm back to square 1,
> probably then I'll have to use the kerneldient filter if my 2500+ can
> take it.

Note that my understanding of the situation is not very solid, but I have
found numerous references on the web to (unfixable) tearing problems when
running with twinview on GF4 cards.  I would be *very* interested in a
solution to this problem, if you or anyone else manages to find one!  As for
your setup, if I understand what you are trying to do, running the
experiment with the dvi output on your new video card should hopefully tell
us a lot about what is going on here.

Peter